Chromatography is a separation method based on different retentions of compounds of a mixture on a stationary phase. The compounds are separated by percolating a liquid, gaseous or supercritical eluent in a device (in general a cylindrical column, or one with another geometry) filled with stationary phase. The compounds progress more or less rapidly in the column depending on their displacement kinetics and on their affinity with the chromatography support. Thus, they get more or less separated.
This method is widely applied as an analysis technique in order to identify and quantify components in a mixture. It is also widely used as an industrial purification technique.
As the chromatography column is filled with a stationary phase, this is where the separation of the different compounds takes place. When the separation is carried out, the compounds and the eluent should therefore be introduced into the column, and then extracted therefrom. To this end, supply and collection systems are used, placed at the input and at the output of the column, through which fluids travel during separation.
An industrial chromatography column generally consists of a cylindrical barrel closed on each side by floors. Optionally a piston may replace one of the floors, in certain applications, notably pharmaceutical applications.
The column is filled with a stationary phase (generally beads having an average size of a few micrometers to a few millimeters depending on the applications) through which compounds to be separated and the eluent percolate. One or several separation cells may be present in a same column. The supply and collection networks are located on the floors of the column and support the stationary phase of each separation cell. These networks are also used for distributing and collecting fluids on the entire surface of the stationary phase at any time, as uniformly as possible. Separation efficiency is therefore influenced by the design of these networks, since it is necessary to inject an eluent from a conduit on the whole surface of the column floor or to draw off this eluent from the floor to a conduit. The supply and collection networks are designated a distributor or distribution network, without any distinction.
Documents U.S. Pat. No. 5,354,460, WO 99/48599, US 2007/0246428 and US 2006/124550 disclose designs in which the fluid injected into the network is oriented via distribution channels of approximately equal lengths to one or several sub-distributors in order to ensure an approximately identical injection time for all current lines on the stationary phase. Thus, quasi-uniformity of travel distances for a given compound between its entry point into the column and its injection strictly speaking onto the stationary phase is ensured. These systems nevertheless entail a significant cost related to the manufacturing of these networks when the columns have a large diameter, because of the multiplication of the sub-distributors.
Document WO 02/92188 discloses a distribution system with several stages, wherein the input or output flow is divided at each stage in two concentric grooves (case of cylindrical columns) or perimeter grooves (case of columns having a square section), which may optionally be subdivided in the next stage, so as to allow the fluid to travel a relatively homogenous distance before reaching the bed of stationary phase. This type of system may also entail a significant cost because of the complexity of the distributor with several stages, and it induces a loss of efficiency in certain cases.
Document WO 2006/055222 discloses distributors between the cells of a column, which consist of one or several upper grids (or perforated plates) supporting the bed of particles, of one or several deflection plates, and one or several lower grids (or perforated plates) making it possible to ensure distribution of the liquid before percolation in the lower cell. In these distributors, a space separates the deflection plate(s) of the lower grid(s).
Document FR 2 933 000 discloses a system of the same type, in which a baffle may be inserted in the distributor, in order to homogenize the length of the flow lines in each separation cell and to reduce dispersion.
These distributors have a large volume of liquid because of the interstitial spaces, which increases the dispersion of the fluid and reduces separation efficiency.
Documents WO 00/50144 and WO 2011/159232 disclose distributors of a generally conical shape. In some cases, the volume inside the distribution cone may be filled with a porous material. These distributors also have a large volume, and the cost for manufacturing the floor (by forging and/or machining) and optionally the interstitial porous material is generally high.
In the context of industrial chromatography columns of so-called “high performance”, i.e. equipped with at least one movable piston and using particles of small dimensions (in general from 5 to 50 μm), and having a reduced overall size (typically of the order of a maximum diameter of 1 meter), the fluid is injected through a central conduit (or several injection points distributed on the diameter) into a compression chamber of a small thickness (generally a few mm), adjacent to a floor or a machined piston. The fluid is subject to pressure generated by a resistive distributor (generally a superposition of low porosity grids).
This resistive system of a small volume forces the fluid to be distributed in the compression chamber within a very short time, which provides quasi-uniform injection on the stationary phase. In order to ensure a constant thickness of the compression chamber, the ends of the column (floor or piston) consist of assemblies of accurately machined parts which are not welded together.
This device can however not be contemplated for columns of large diameter for which the floors are maintained by welding at the barrel of the column. Indeed, the barrel of the column is made in a rolled and welded metal sheet to which the floors (at the ends or intermediate between both cells) are then also welded. By design, the horizontality and the height of the floor are not controlled and the floor has surface undulations of a few millimeters. This distribution method therefore seems to be incompatible with the columns of large diameter.
There is a need for columns (notably of a large diameter) of the chromatography column type, equipped with fluid distributors allowing efficient fluid distribution over the whole surface of the column, and of a simpler design (and therefore entailing less cost) than the columns of the state of the art. It is also desirable to facilitate the assembling and maintenance operations.